1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a semiconductor device having an insulating film of superior properties formed on the surface of Al.sub.x Ga.sub.1-x As (0.ltoreq.x.ltoreq.1) and a method of manufacturing the same.
2. Description of the Related Art
Forming insulating films of superior properties on Al.sub.x Ga.sub.1-x As surface has been impossible heretofore. A metal/insulator/semiconductor (MIS) structure of such fine properties as obtained by Si MIS integrated circuit technique has been impossible in the case of Al.sub.x Ga.sub.1-x As.
An MIS structure is one of the fundamental structures of semiconductor devices. The properties of an MIS structure depend on the characteristics of an insulating film itself. Further, they depend greatly on the properties of an interface between an insulating film and semiconductor, particularly on the concentration of the interface states.
An Si MIS structure has excellent properties in terms of interface state density, leakage current, trap concentration in insulator, reliability, and the like because a Si insulating film provides ideal properties, having thus contributed much to the development of integrated circuit devices.
A good MIS structure for the typical III-V compound semiconductor GaAs is still not available in spite of intensive studies over a long period of 20 years or more.
Absence of a good MIS structure is a main obstacle against the development of various GaAs devices. An advent of a good MIS structure has long been desired by device designers, developers, and other engineers.
in GaAs MIS structures developed to date, most of insulating films have been silicon oxide (SiO.sub.x) films, silicon oxynitride (SiO.sub.x N.sub.y) films, and GaAs oxide films (Ga oxide and As oxide).
Each of these MIS structures has a number of interface states at the interface of an insulating film and a GaAs layer. Several abnormalities in the electric characteristics of the MIS structure have been observed.
FIGS. 5A and 5B show the capacitance-voltage (C-V) characteristics of conventional MIS diodes which use GaAs oxide films as insulating films, the abscissa representing an applied voltage V and the ordinate representing a capacitance pF.
The sample used for the measurement of FIG. 5A shows no change in the capacitance relative to an applied voltage. Since the width of a depletion layer on the semiconductor surface of the sample does not change, it is almost impossible to manufacture MIS field effect transistors.
The sample used for the measurement of FIG. 5B shows a large hysteresis of the C-V characteristic, and large frequency dispersion is observed on the accumulation side. It is difficult for such samples to obtain a definite response to an applied voltage. Since the frequency characteristic is not good, it is very difficult to obtain high speed semiconductor devices.
Most of conventional MIS insulating films have been associated with a large diode leakage current. A poor insulating performance is not suitable for gate insulating films, nor for surface passivation films.
It is considered that the above-described abnormalities result from a number of traps in an insulating film and from a high concentration of the interface states between an insulating film and GaAs.